1. Microevolution
Chapter 16

2. Selective Breeding & Evolution
Evolution is genetic change in a line of descent through successive generations
Selective breeding practices yield evidence that heritable changes do occur

3. Evolutionary Theories
Widely used to interpret the past and present, and even to predict the future
Reveal connections between the geological record, fossil record, and organismal diversity

4. Early Scientific Theories
Hippocrates - All aspects of nature can be traced to their underlying causes
Aristotle - Each organism is distinct from all the rest and nature is a continuum or organization

5. Confounding Evidence Biogeography Comparative anatomy
Geologic discoveries

6. Biogeography
Size of the known world expanded enormously in the 15th century
Discovery of new organisms in previously unknown places could not be explained by accepted beliefs
How did species get from center of creation to all these places?

7. Comparative Morphology
Study of similarities and differences in body plans of major groups
Puzzling patterns:
Animals as different as whales and bats have similar bones in forelimbs
Some parts seem to have no function

8. Comparative Anatomy
Python
Human

9. Geological Discoveries
Similar rock layers throughout world
Certain layers contain fossils
Deeper layers contain simpler fossils than shallow layers
Some fossils seem to be related to known species

10. The Theory of Uniformity
Lyell’s Principles of Geology
Subtle, repetitive processes of change, had shaped Earth
Challenged the view that Earth was only 6,000 years old

11. Malthus - Struggle to Survive
Thomas Malthus, a clergyman and economist, wrote essay that Darwin read on his return to England
Argued that as population size increases, resources dwindle, the struggle to live intensifies and conflict increases

12. Darwin’s Voyage
At age 22, Charles Darwin began a five-year, round-the-world voyage aboard the Beagle
In his role as ship’s naturalist he collected and examined the species that inhabited the regions the ship visited

13. Voyage of the Beagle
EQUATOR
Galapagos
Islands

14. Galapagos Islands Volcanic islands far off coast of Ecuador
Darwin
Wolf
Pinta
Marchena
Genovesa
Fernandia
Santiago
Bartolomé
Rabida
Pinzon
Seymour
Baltra
Santa Cruz
Santa Fe
Tortuga
Española
San Cristobal
Floreana
Volcanic islands far off coast of Ecuador
All inhabitants are descended from species that arrived on islands from elsewhere
Isabela

15. Glyptodonts & Armadillos
In Argentina, Darwin observed fossils of extinct glyptodonts
Animals resembled living armadillos

16. Galapagos Finches
Darwin observed finches with a variety of lifestyles and body forms
On his return he learned that there were 13 species
He attempted to correlate variations in their traits with environmental challenges

17. Darwin’s Theory
A population can change over time when individuals differ in one or more heritable traits that are responsible for differences in the ability to survive and reproduce

18. Alfred Wallace
Naturalist who arrived at the same conclusions Darwin did
Wrote to Darwin describing his views
Prompted Darwin to finally present his ideas in a formal paper

19. Populations Evolve Biological evolution does not change individuals
It changes a population
Traits in a population vary among individuals
Evolution is change in frequency of traits

20. The Gene Pool All of the genes in the population
Genetic resource that is shared (in theory) by all members of population

21. Variation in Phenotype
Each kind of gene in gene pool may have two or more alleles
Individuals inherit different allele combinations
This leads to variation in phenotype
Offspring inherit genes, NOT phenotypes

22. What Determines Alleles in New Individual?
Mutation
Crossing over at meiosis I
Independent assortment
Fertilization
Change in chromosome number or structure

23. Microevolutionary Processes
Drive a population away from genetic equilibrium
Small-scale changes in allele frequencies brought about by:
Natural selection
Gene flow
Genetic drift

24. Gene Mutations Infrequent but inevitable
Each gene has own mutation rate
Lethal mutations
Neutral mutations
Advantageous mutations

25. Hardy-Weinberg Rule
At genetic equilibrium, proportions of genotypes at a locus with two alleles are given by the equation:
p2 + 2pq + q2 = 1
Frequency of allele A = p
Frequency of allele a = q
p + q = 1

26. Sickle-Cell Trait: Heterozygote Advantage
Allele HbS causes sickle-cell anemia when heterozygous
Heterozygotes are more resistant to malaria than homozygotes
Malaria case
Sickle cell trait
less than 1 in 1,600
1 in 400-1,600
1 in
1 in
1 in
more than 1 in 64

27. Hardy Weinberg Analysis
Tropical Africa = 1/60 = .02 q2 = q = p = .994 q = Hbs p = HbA
Elswhere = 1/1000 = q2 = q = p = q = Hbs p = HbA

28. Natural Selection
A difference in the survival and reproductive success of different phenotypes
Acts directly on phenotypes and indirectly on genotypes

29. Basis for Natural Selection
Reproductive Excess
Variation
Struggle for Survival
Survival and Reproduction of the better Adapted.

30. Reproductive Capacity & Competition
All populations have the capacity to increase in numbers
No population can increase indefinitely
Eventually, the individuals of a population will end up competing for resources in order to survive

31. Variation in Populations
All individuals have the same genes that specify the same assortment of traits
Most genes occur in different forms (alleles) that produce different phenotypes
Some phenotypes compete better than others (they are better adapted = have what it takes to survive)

32. Struggle for Survival
Over time, the alleles that produce the most successful phenotypes (best adapted) will increase in the population
Less successful alleles will become less common
Change leads to increased fitness
Increased adaptation to environment

33. Directional Selection
Number of individuals
in the population
Range of values for the trait at time 1
Allele frequencies shift in one direction
Number of individuals
in the population
Range of values for the trait at time 2
Number of individuals
in the population
Range of values for the trait at time 3

34. Peppered Moths
Prior to industrial revolution, most common phenotype was light colored
After industrial revolution, dark phenotype became more common

35. Pesticide Resistance Pesticides kill susceptible insects
Resistant insects survive and reproduce
If resistance has heritable basis, it becomes more common with each generation

36. Antibiotic Resistance
First came into use in the 1940s
Overuse has led to increase in resistant forms
Most susceptible cells died out and were replaced by resistant forms

37. Gene Flow Physical flow of alleles into a population
Tends to keep the gene pools of populations similar
Counters the differences that result from mutation, natural selection, and genetic drift

38. Genetic Drift
Random change in allele frequencies brought about by chance
Effect is most pronounced in small populations
Sampling error - Fewer times an event occurs, greater the variance in outcome

39. Bottleneck A severe reduction in population size
Causes pronounced drift
Example
Elephant seal population hunted down to just 20 individuals
Population rebounded to 30,000
Electrophoresis revealed there is now no allele variation at 24 genes

40. Founder Effect
Effect of drift when a small number of individuals start a new population
By chance, allele frequencies of founders may not be same as those in original population
Effect is pronounced on isolated islands

41. Inbreeding Nonrandom mating between related individuals
Leads to increased homozygosity
Can lower fitness when deleterious recessive alleles are expressed
Amish, cheetahs